1. Field of the Invention
The present invention relates to an outside mirror assembly for use in an automobile which includes an ultrasonic wave generator for removing water drops on the surface of the mirror glass. More particularly, the present invention relates to a mirror glass holding apparatus for holding the mirror grass to which the vibration is applied by the ultrasonic wave generator.
2. Description of the Prior Art
As is well known, when the water drops of rain or fog adhere on the surface of the mirror glass incorporated in the outside mirror assembly for use in the automobile, the mirror glass becomes blurred, naturally. Accordingly, there has been conventionally provided the above described type mirror assembly having an ultrasonic wave generator for removing the water drops on the mirror glass. The mirror glass is vibrated by means of the ultrasonic wave generator mounted behind the mirror glass so that the water drops are splashed out of the surface of the mirror glass.
FIG. 1 is a front view of the conventional mirror assembly of a type as described above, and FIG. 2 is a section taken along a line II--II in FIG. 1. As shown in the figures, a mirror glass 10 is held by a back support or back holder 16. The back holder 16 has a peripheral flange 14 which engages the front surface of the edge of the mirror glass 10. There is provided a supersonic wave generator in the back holder 16 and behind the mirror glass 10. The supersonic wave generator comprises a vibration element 18 and a vibration plate 20 which is driven by the vibration element 18 to cause the vibration of the mirror glass 10. When the vibration of the vibration element 18 is transmitted to the mirror glass 10 via the vibration plate 20, the mirror glass 10 vibrates to splash the water drops on the surface thereof.
Meanwhile, according to the conventional apparatus the water drops D2 caught in a gap between the flange 14 and the edge of the mirror glass as well as the water drops D1 on the center side of the mirror glass 10 are splashed, as shown in FIG. 2, so that the splashed water drops D2 disadvantageously adhere again onto the surface of the center side of the mirror glass 10.
In the conventional apparatus, the gap between the flange 14 and mirror glass 10 is generally set at a very small value, for example below 0.1 mm in order that the mirror glass 10 can be surely secured by the flange 14 or the back holder 16.
The inventors of the present invention have conducted an investigation into the cause of the phenomena of splashing water drops from the edge of the mirror glass 10 and had the following result. Namely, the inventors have found a fact such that the gap volume defined by the flange 14 and the mirror glass 10 is altered continuously due to the vibration of the mirror glass 10, resulting in a production of a pumping action for splashing the water drops D2.
In order to solve the conventional disadvantage, the gap between the flange 14 and the mirror glass 10 might be reduced to prevent the pumping action. In this case, however, the mount of the mirror glass 10 is loosened disadvantageously and a cavitation might be generated in the water drops D2 so as to splash the water drops D2.